This invention relates to the feeding of particulate matter into a high pressure zone, and in particular to a screw feed apparatus frequently known as a solids pump.
There are occasions such as introducing pulverized coal into a high pressure air stream where it is necessary to pump the coal to this high pressure level. This has been done with screw pumps where a helical member having flights is rotated within a cylinder, and the coal is supplied to the upstream end of this cylinder. These pumps operate at high speed (over 900 rpm).
In some cases a reducing pitch is used so that the coal is compacted as it travels through the cylinder, becoming sufficiently compacted that the high pressure air cannot leak back through the coal. In other cases a reducing nozzle is located at the outlet end so that the coal is compacted as it pushes through the nozzle thereby forming a seal at that location.
Those pumps we have been able to find which are capable of sealing against a reasonable back pressure have suffered from the disadvantage of high power consumption.